John Gill Commentary Numbers 35:18

"Or if he smote him with a weapon of wood in the hand, whereby a man may die, and he died, he is a murderer: the murderer shall surely be put to death." — Numbers 35:18 (ASV)

Or if he smote him with an hand weapon of wood
A stick, or staff, or club:

wherewith he may die, and he die ;
which is sufficient to kill a man, as the same Targum explains it; and a man dies with the blow that is given him by it:

he is a murderer, and the murderer shall surely be put to death ;
no pardon given him, or the benefit of the city of refuge allowed him.